The advent of the computer has already had a profound effect upon human society, and the impact of processing technology is expected to increase. Indeed, the desirability to store information for subsequent retrieval currently grows at an exponential rate. Thus, various types of devices have been developed to store data both for on-line usage as well as for archival purposes.
Where on-line processing requires data to be readily at hand, a significant improvement was provided by the advent of the magnetic disk storage array. Here, one or more magnetic disks are provided, and a read/write recording head is used to record information on the disk as well as to retrieve information or data for use by the computer processor. Significant strides have been made in the ability to increase the density of data stored on such magnetic disk arrays.
In order to gain an even higher density for on-line data, the optical disk was developed. These devices record data based upon a very small wavelength of light so that a higher density is obtained due to this technique. Laser light is employed to read the stored information or data on the optical disk. However, once imprinted, the disk presently cannot be rewritten although significant research is underway in an effort to develop such technology.
In early days of the computer, before the advent of the magnetic disks and the optical disk storage assemblies, data was typically stored on magnetic tapes, such as reel-to-reel tapes and later cassettes. In a magnetic tape storage device, a magnetic coil is used as a transducer both to imprint data magnetically on a moving band of magnetic film; thereafter, when the film is advanced across the transducer, the data may be read and re-input into a co-processor. Magnetic tape can be erased and rewritten many times and has an advantage of low cost.
Magnetic tape is still a highly desirable format for archiving data for rapid access is of less significance and cost is of concern. However, where vast quantities of data are to be maintained, these tapes can be bulky due to the physical number necessary to store the quantity of data. The capacity for such tapes to store data, of course, is dependent upon the number of "tracks" which can be independently placed across the width of the tape. Thus, for example, a magnetic tape read/write system that is able to read and write nine tracks of data on a single strip of tape will hold four and one-half times the amount of data as a system which only utilizes two tracks. Therefore, efforts to increase the capacity of magnetic tapes to store data have included substantial efforts to increase the number of tracks which can be written on a band of magnetic tape.
In order to increase the density of data stored onto a magnetic tape, one technique has been to support a plurality of individual read/write transducers in an array on the read/write recording head. For example, where eight transducers are placed side-by-side across the head, eight tracks can be simultaneously written or read as the tape is translated across the head and the tape advance direction. In order to provide this number of transducers, however, they may need to be very small in size. Importantly, the reduction in size of the transducer results in a substantial portion of unused magnetic tape in bands extending parallel to and in between each recorded tack. Therefore, in order to further increase density, it is now a common practice to write data in between the tracks so that, for example, a tape head that includes eighteen transducers may be first used to record a set of eighteen tracks after which the tape may be rewound and the head shifted half of the distance between the tracks and a set of eighteen more tracks recorded for a total of thirty-six tracks on the tape band. The ability to create multi-track storing, then, becomes dependent upon the precision with which the tape head may be translated to create the different sets of tracks.
In the typical technique for translating a read/write recording head employs a lead screw that is threaded into a threaded nut associated with the tape head. Rotation of the threaded shaft, for example, by a stepper motor, then can translate the tape head a desired distance. While this technique is useful in increasing the ability to do multi-track recording, a lead screw assembly includes an inherent "sloppiness" as a result of the need to have some gaps between the lead screw threads and the threads to avoid binding during use. In order to compensate for this sloppiness, it is known to use threaded lead screws wherein ballbearings reside in the threads to help to remove the sloppiness. While this technique does increase precision, a lead screw assembly necessarily has a large mass so that, as the tape head is shifted, substantial momentum and energy must be overcome, especially at the extrema of the translated distance.
In addition to the use of lead screws, it has been known to use camming structures as a mechanism for translating a read/write recording head transversely across a tape medium so as to read multiple discrete tracks on such tape. One such example is shown in U.S. Pat. No. 3,705,270 issued Dec. 5, 1992 to Huber. In this patent, a read/write recording head is secured to a carriage which slides on a pair of rails so that the read/write head may translate transversely across the tape. The carriage is biased for abutment against a spherical cam follower that is sandwiched between the carriage and a rotatable cam. The cam has a plurality of steps that provide incremental movement of the read/write recording head.
U.S. Pat. No. 3,839,737 issued Oct. 1, 1974 to Vogel also employs a stepped cam to move a read/write recording head transversely of the tape medium. Here, however, the cam follower is in the form of a following post that rides on the surface of the cam. U.S. Pat. No. 3,370,131 issued Feb. 20, 1968 to Reed also shows a pin type cam follower that moves a transducer. In the Reed Patent, however, the cam surface is an inclined plane without discrete steps. Movement of the cam surface is accomplished by a rack and pinion gear assembly.
In my co-pending application Ser. No. 08/588,211 filed Jan. 19, 1996, and now U.S. Pat. No. X,XXX,XXX, a positioning assembly utilizing a cam in the form of either a continuous cam surface, a stepped cam surface or a cam employing individually sized bearings is disclosed for the precise adjacent of a follower shaft that supports a read/write recording head. This patent application recognized the need to prevent angular rotation of the read/write recording head during translational movement, and the patent application discloses a mechanical structure for preventing angular rotational movement during reciprocal translation of the read/write head.
Despite the development of the above described positioning devices, there remains a need for head positioning assemblies that are increasingly more precise in positioning a read/write head on a multi-track recording medium so as to allow an increasingly large number of tracks to be introduced on and read by such a recording head. There has been a further need for simplified structures and recording devices which use these structures. There has been a particular need for positioning structures for read/write recording heads that reduce or eliminate angular rotation of the read/write head during translational movement without impeding such translational movement.